This invention relates to ignition timing control for an internal combustion engine.
JP-A 2001-82302 published by the Japanese Patent Office in 2001 discloses a control device which uses rotation speed as a parameter in order to calculate an ignition timing.
The ignition timing is calculated and set on the basis of successive REF signals defining a reference position of the crankshaft. The REF signals comprise a detection signal from a crank angle sensor. As a result, particularly when starting the engine, during transient operating states in which the engine rotation speed increases rapidly from a low rotation speed in a short period, the fluctuation in the rotation speed between the interval of the input of REF signals increases, consequently the problem arises that a required ignition advance can not be obtained.
The dimension of the advance per ignition signal control cycle is restricted by an advance limit. If the engine rotation speed reaches a certain speed and the advance per control cycle is increased, there is the possibility that misfiring will occur due to an insufficient current-carrying angle (dwell angle) in the primary current. This result may be prevented by restricting the advance by providing an advance limit. However during large fluctuations in the rotation speed, it is not possible to perform an advancing operation up to an optimal ignition timing (for example, an MBT minimum advance for best torque) due to the limit on the advance. As a result, optimal combustion conditions can not be realized.
Furthermore if the engine rotation speed is represented as a REF signal, and in particular, when the REF signal comprises a long time interval such as that during startup, the deviation of the actual rotation speed from the rotation speed calculated using the REF signal increases and generally the rotation speed appears to decrease. Consequently the generated torque may be reduced due to the fact that the calculated ignition timing tends to act as a retard on the optimal ignition timing. Alternatively, the generated torque may be reduced as a result of the calculated current-carrying time shortening relative to an optimal current-carrying time and thus resulting in a reduction in the ignition energy.
Decreases in torque during transient operating states result in adverse effects on performance and in particular, constitute a cause of adverse effects on exhaust emission control and startability during startup conditions.
It is therefore an object of this invention to enable rapid advancing operations up to a suitable ignition timing during transient operating states including engine startup.
In order to achieve the above object the invention provides an ignition control device for an internal combustion engine, the internal combustion engine comprises a spark plug provided in a combustion chamber and an ignition coil supplying an ignition current to the spark plug, the ignition coil controlling an ignition current supplied to the spark plug based on a supplied primary current. The ignition control device comprises a first sensor detecting a rotation speed of the engine crankshaft, a second sensor detecting a transient operating state of the engine; and a controller. The controller functions to determine a transient engine operating state based on the output of the second sensor; calculate the basic ignition timing based on the rotation speed; set an advance limit which is the maximum value of the advance on the ignition timing to a different value during a transient operating state and during a steady-state operating state, the value during a transient operating state being the larger value; set the ignition timing by using the limit to restrict the advance on the basic ignition timing, the basic ignition timing being calculated based on the rotation speed; calculate a dwell angle comprising the period of application of an ignition current in response to the rotation speed; and control the primary current supplied to the ignition coil based on the ignition timing and the dwell angle.
The details as well as other features and advantages of the invention are set forth in the remainder of the specification and are shown in the accompanying drawings.